Effects of In Ovo Methionine-Cysteine Injection on Embryonic Development, Antioxidant Status, IGF-I and TLR4 Gene Expression, and Jejunum Histomorphometry in Newly Hatched Broiler Chicks Exposed to Heat Stress during Incubation

SIMPLE SUMMARY: In the current study, we hypothesize that the In ovo concurrent injection of methionine (Met) and cysteine (Cys) may have positive effects on embryonic development, insulin-like growth factor-I (IGF-I) and toll-like receptor-4 (TLR4) gene expression, antioxidant status, biochemical profile, and jejunum histomorphometry of newly hatched broiler chicks exposed to heat stress during the incubation period. As indicated, the In ovo injection of Met and Cys resulted in increased hatch weight, higher levels of total antioxidant capacity, and glutathione activity in the serum and tissues. At the same time, a decrease in the level of heat shock protein-90 and an increase in TLR4 and IGF-I expression in the tissues was observed. In addition, the In ovo injection of Met and Cys improved jejunum histomorphometric parameters of newly hatched broiler chicks. Generally, the concurrent In ovo injection of Met and Cys improved broiler embryonic development, antioxidant status, TLR4, and IGF-I expression and jejunum histomorphometric parameters in newly hatched broiler chicks exposed to heat stress conditions during incubation. ABSTRACT: Sulfur amino acids are typically the first-limiting amino acids (AA) used in protein metabolism in poultry. Therefore, we hypothesized that their utilization in the pre-hatch period would affect embryonic development, IGF-I and TLR4 gene expression, antioxidant status, serum biochemical profile, and jejunum histomorphometry of newly hatched Ross broiler chicks incubated under heat stress conditions. A total of 150 fertile broiler eggs were subjected to heat stress (39.6 °C for 6 h/d) from d10 until d18 and injected at d 17.5 of incubation with methionine and cysteine (Met-Cys) at a dose of 5.90 mg l-methionine plus 3.40 mg l-cysteine. The effects of Met-Cys administration were examined and compared with the control (Non-injected group) and 0.75% NaCl injected group. The results showed that no significant differences among all groups in serum protein profiles (total protein, albumin, globulin, and albumin/globulin ratio) and creatine kinase were observed. The level of heat shock protein-90 was decreased with Met-Cys In ovo injection. The In ovo injection of Met-Cys also improved the values of total antioxidants capacity and glutathione in examined tissues. At the same time, an increase in fold change mRNA abundance of IGF-I and TLR4 was observed after Met-Cys injection in tested tissues. Finally, an increase of 29% in villus area was found after Met-Cys injection compared to the control group. In conclusion, the In ovo injection of Met-Cys resulted in improved embryonic development, IGF-I and TLR4 gene expression, antioxidant status and jejunum histomorphometry of newly hatched broiler chicks exposed to heat stress during incubation.